Evaluation of Oral Health Status Based on DMF Index in Adults Aged 40-70 Years: Findings from Persian Kharameh Cohort Study in Iran

Statement of the Problem: Oral health is one of the most important public health problems. The DMF index is used to assess oral health status. Purpose: This study was performed to evaluate oral health status based on DMF index in adults in Fars province. Materials and Method: This cross-sectional study was performed on 8911 people aged 40 to 70 years under the Kharameh cohort study in 2020. Demographic and oral health factors were collected during interviews and clinical evaluation. T test, ANOVA, and linear regression tests were used for data analysis. Results: The mean and standard deviation of DMF index was 18.06±8.7in all individuals under study. Multiple linear regression results showed that diabetes (OR=1.1 95%CI: 0.9-1.9 p= 0.0001), smoking (OR=4.4 95%CI: 4-4.9 p= 0.0001) and underweight (OR=2.1 95%CI: 1.1-3.1 p= 0.0001) are the factors affecting the increase in DMF index. Other factors such as high level of education, economic and social class, flossing, and living in a village have been inversely related to the DMF index. Conclusion: The results of this study are a warning about the importance of reducing dental costs to increase the level of access of people with low economic and social levels and increase health literacy in relation to oral health.


Introduction
Oral health is a crucial component of public health [1] that is directly related to people's health [2][3]. It affects many personal activities such as eating, talking, social communication and quality of life, to the extent that the World Health Organization has identified oral health as one of the most prevalent and important public health problems [4], Oral health includes a wide range of oral diseases, one of which happens to be tooth decay [5].
Tooth decay is a major public health concern [6][7] affecting people of all ages, genders, races and economic and social classes [2]. According to the World Health Organization, approximately 3.5 billion people, 35.5% of the total population, have permanent tooth decay [8].
Furthermore, about 30% of people aged 65 to 74, worldwide, do not have any healthy teeth [4]. The prevalence of tooth decay is also high in Iran. The findings of a national study conducted between 2001 and 2002 in Iran showed that the average tooth decay in 18-yearolds was 3.4 and in 35-45-year-olds; it was 11 times higher than that of everyone else [4].
Tooth decay occurs when pathogenic bacteria has covered the tooth surface [6]. Although reversible in the early stages, it progresses slowly and destroys hard tooth tissue if left untreated [9]. This can even lead to tooth loss, which in turn causes malfunction and social discomfort to people affected [10]. Tooth decay is a multifactorial disease [7], which mostly depends on eating habits such as sugar intake and individual behaviors [3]. In several studies conducted around the world, various factors have been identified in the prevalence of tooth decay, including: gender [11], age [12], level of education brushing [4], smoking [13], environmental factors [14] and economic and social class [11].
The most important indicator used to assess oral health status is the DMF index [4], which is recommended by the World Health Organization to determine and compare the rate of tooth decay in a population [15]. This index shows the number of decayed, missing and filled teeth and is used to evaluate and control oral health interventions, design policies, and implement interventional programs. Most epidemiological studies in this regard focus on children [6], thus adults have received less attention [4]. Nonetheless, evaluating adults' oral health status is essential for planning and performing appropriate interventions for the development of oral health policies. Therefore, this study aimed to evaluate the oral health status in adults residing in Kharameh city of Fars province.

Materials and Method
The present study is a cross-sectional descriptiveanalytical study conducted using baseline data from the Kharameh cohort study (Fars province-Iran) yielded from 8911 individuals aged from 40 to 70 years old in 2020. Kharameh population-based cohort study is a part of the Persian Cohort study in Iran, which aims to investigate the risk factors for non-communicable diseases in their subjects. After obtaining consent from individuals, questionnaires were administered by trained health-care staff during face-to-face interviews. All demographic information, disease status, economic and social status and lifestyle and behavioral factors were collected during the interviews, following a clinical examinations and anthropometric measurements performed for all subjects. Other details of cohort studies can be seen in other publications [16].
The information required for this study included demographic information such as age, sex, body mass index, level of education, place of residence, smoking habits, economic and social status and diabetes history.
In addition, other required data included the infor- To assess the oral health status of the subjects the DMF index was used. This index was calculated based on the results of examining the condition of the teeth in terms of the number of decayed, filled and missing teeth. Oral and dental examinations were performed by trained dentists on field, using a probe, mirror and cotton rolls, in order to score each participant using the DMF index. Finally, frequency and standard deviation were used to describe quantitative variables, and frequency or frequency percentage was used for qualitative variables. After examining the normality of variables, if normal, t-test was used to examine the difference between mean DMF indices between two groups, and if not normal, Mann-Whitney test was used. Furthermore, to evaluate the difference between the mean DMF indices in more than three groups, ANOVA statistical test was applied for normal data and if not normal, Cross-Wallis test was used. To detect differences in between groups, Bonferroni test has been used. Additionally, in order to identify the factors affecting the increase in DMF index, simple and multiple linear regression was applied. Significance level was considered less than 0.05 for all tests and all analyses were performed using the STATA version 13 software.

Results
The present study was performed on 8911 individuals aged between 40 to 70 years old from the Persian Kha-and 56.6% were female. 46% of people were in the age group of 40 to 50 years old, 34.4%, 50 to 60 years old and 19.5%, 60 to 70 years old. 65.3% of subjects did not use a toothbrush; only 28.2% brushed once a day, 5.8% twice a day, and 2.3% of people brushed three times a day. Further demographic and oral health information of the subjects are shown in Table 1.
Based on the results of this study, the mean and standard deviation (SD) DMF in all subjects was 18.    Table 3.

Discussion
In this study, the mean DMF index (standard deviation) in all subjects was 18.06±8.7. Although, no statistically significant difference between the mean DMF in the age These can be effective in reducing this difference.
Mean DMF index in this study was higher than other previously conducted similar studies. In a previous study conducted in Iran's Kurdistan, the DMF index mean in the age group of 35 to 45 years was equal to 7.8 [4], and in another study this number was in Iran 14.8.
In Japan 12.2, Malaysia 12.1, South Korea 5.2 and Turkey 10.8 [17]. Additionally, in a study conducted in Kosovar, the mean DMF index was 11.6 for people aged 35 to 44 and 13.6 for people aged 45 to 65 [6]. In eastern China this number was 3.5 [18], in Italy 4.3 [11] and 14, between Greece's 35-75 years old population [14]. This difference in the average DMF index could be due to cultural, economic and social differences as well as access to oral health services and healthcare in general in the study location. Another reason could be attributed to the differences existing in these populations given that they could not be completely similar.
Higher education, economic and social levels in our study reduced the DMF index, in consistency with the results of many other prior studies [20][21]. Research carried out in Greece [14], Italy [11] and between 20 to